Hot melt adhesives are typically thermoplastic adhesives that are solid at room temperature and melted prior to use. Hot melt adhesives may be used during such diverse activities such as building construction, shoe manufacture, and book binding. In addition, many uses exist in the assembly of automobile parts, electronics, electrical equipment, appliances, electrical components, furniture and other widely ranging manufacturing processes. The common forms of hot melt adhesives include, for example, polyamide adhesives, pressure sensitive adhesives (PSA), ethylene vinyl acetate (EVA), polyurethane reactive (PUR) adhesives, and other types of adhesives. The present invention is especially applicable to PUR adhesives, however, its various aspects are applicable to other types of meltable thermoplastic materials as used in many circumstances, such as those mentioned above.
Clean up and maintenance procedures of adhesive dispensing systems are always important considerations in a manufacturing environment. PUR adhesives present additional problems and challenges in that these adhesives are moisture curable and are generally not easily cleaned or flushed from a dispensing system having a large number of small precision parts and passages. Thus, dispensing systems are especially difficult to clean and maintain when used with PUR hot melts and are therefore more likely to require increased down time and maintenance. This results in higher manufacturing costs.
Various components in an adhesive dispensing system will require cleaning and maintenance including adhesive distribution bodies such as the manifold or service block associated with a dispensing apparatus. Such an apparatus typically includes at least one dispensing module having an internal valve element for selectively opening and closing a discharge passage and thereby either allowing or preventing the discharge of adhesive in a desired manner. The module is often operated pneumatically, although electrically operated modules also exist. At least one module is mounted to a manifold or service block which supplies at least the molten hot melt adhesive to the valve module and, if pneumatically operated, may also supply air for operating the valve element within the module. In addition, if the valve module utilizes process air, for example, to produce a particular adhesive spray pattern, the process air may also be provided through the manifold or service block.
In view of the current challenges associated with cleaning and maintaining apparatus for dispensing thermoplastic material, it would be desirable to provide such apparatus, including service blocks, manifolds or other material distribution bodies in the dispensing system, with more easily cleanable and/or maintainable material supply and distribution passages in order to decrease cleaning and maintenance costs and the downtime associated with these procedures.